A. Technical Field
The present invention relates to a hydrophilic graft polymer, a production process therefor, a composition containing the hydrophilic graft polymer, a scale inhibitor comprising the hydrophilic graft polymer, and a scale inhibition method using the hydrophilic graft polymer.
B. Background Art
A hydrophilic graft polymer, as obtained by graft-polymerizing an unsaturated carboxylic acid type monomer such as (meth)acrylic acid onto a polyether compound, is used alone or in the form of a composition for a scale inhibitor or for various other purposes. For example, compositions, comprising the following components: the above-mentioned hydrophilic graft polymer, the polyether compound which is a raw material thereof, and an unsaturated carboxylic acid type polymer which is a by-product in the production of the hydrophilic graft polymer, are disclosed in JP-A-55-71710, JP-A-59-62614, and JP-A-7-53645, and are applied for various uses such as detergent builders and dispersants of organic particles and inorganic particles.
However, any of the above-mentioned known compositions has problems in that dispersibility and gelation resistance are both low, and where they are applied for the above-mentioned uses, the desired performances cannot sufficiently be obtained. In addition, their viscosity is high and they are difficult to handle.
On the other hand, from the circumstances that water having high concentration of calcium carbonate or the like is used as a circulating water for efficiency of utilization of water resources, it is recently required for a scale inhibitor to have a high scale inhibition effect. The above-mentioned known compositions are also used as the scale inhibitor, but the scale inhibitability thereof is low, which do not satisfy a recent high scale inhibition standard.
As to conventional production processes for the above-mentioned hydrophilic graft polymer, the graft ratio of the unsaturated carboxylic acid type monomer to the polyether compound is low, and a large amount of polyether compound as used as the raw material remains unreacted. Therefore, there are problems in that any of the resultant hydrophilic graft polymers has poor purity, and in that where such polymers are used for the above-mentioned uses, the desired performances cannot sufficiently be obtained.
In a cooling water system, a boiler water system, a seawater desalting apparatus, a pulp digester, a black liquor concentrating tank, an oil field, and the like, precipitates (scales) such as calcium carbonate, calcium phosphate, zinc hydroxide, and magnesium silicate deposit on their inner walls, and as a result, various operational difficulties might occur such as decrease in heat efficiency or local corrosion.
In particular, where pipings made of iron are used in an aqueous system, there is the necessity to use a large amount of phosphoric acid compound, zinc salt, or the like as a corrosion inhibitor. In this case, formation of scales comprising calcium phosphate or zinc hydroxide causes problems.
U.S. Pat. No. 4,659,481 specification describes that a polymer comprising a monomer component having hydroxyl group and a monomer component having sulfonic acid group has an effect to inhibit scales of calcium phosphate, zinc hydroxide, or the like.
However, although such a polymer has an effect to some extent in inhibition of scale, since a monomer component having a specific structure is used, there is a problem in that the synthesis thereof is difficult.